Process of hermetic sealing of an evacuated enclosure, applying in particular to theluminescent discharge tubes



Oct. 31, 1950 P. DUSSAUSSOY 2,528,217

PROCESS OF HERMETIC SEALING OF AN EVACUATED ENCLOSURE, APPLYING INPARTICULAR TO THE LUMINESCENT DISCHARGE TUBES Filed Oct. 6, 194'! PIERREDUSSAUSSOY E T R- fiwh Q 0 1i] ATTORNEY Patented Oct. 31,1950

PROCESS or IlERMETIC SEALING OF AN "EVACUATED ENCLOSURE, APPLYING INCHARGE TUBES QPARTICULARTO THELUMINESGENT s-1 I Pierre "Dussaussoy,Paris; France, assigno'r to Compagnie Generale De Telegraphic Sans Fil,

I a corporation of France Application October 6, 1947;.seria1No.778,210. In France November 26, 1946 f? My invention relates-to aprocess of execution of an hermetic sealing between an evacuated en-.closuraor bulb and the extremity of an exhaust .tube which constitutesa stem for the. said bulb.

In the sealing processes of the edge to edge seal 3 Claims. (0.250419type heretofore utilized for the discharge tubes,

a rough provisory seal is first utilized between the tube and the stem,through heating by a flame, and there remains to be realized thetightness of the seal thus obtained, which i shaped by a further heatingoperation carried out in a flame at a relatively hightemperature, of theorder of 900-950", accompanied by ablowing of air inside the tube foravoiding deformation of the latter.

This second operation of heating results in developing mechanicalstresses which compromise the tightness of the tubes, especially iftheir leading-in wires extend through the glass enclosure:

in the immediate neighborhood ofthe stem, such stresses being, moreover,hardly tolerable in the tubes which contain fragile components.

My invention does away with these drawbacks: It consists in proceeding,after the execution of a rough assembly seal, instead of shaping the abulb as I have mentionedabove, in placing, at

the'spot reserved to the seal, a fusible glass (or enamel) havingpractically the same dilatation coefficient as the assembled pieces, andin making it flow through a moderate heating (for instance at atemperature of the order of 550 C.).

It appears therefrom that the process of my invention is simpler thanthe prior processes (since it needs no special shaping and no blowing ofair). On the other hand, by the fact that my process uses a heating ofless intensity and shorter duration, it does not risk to injure theinternal components of the tube, nor to alter the shape of the-glassparts, and moreover it does not result in a defective tightness due tomechanical stresses-the duty of mechanically supporting the componentsof the device being incumbent upon the glass and not upon the enamel.

My invention will be more clearly understood by reference to theaccompanying drawings which set forth my invention in an illustrativesense and not in a limitative sense as applied to a process of making anelectronic discharge tube wherein the lead-in wires extend through thetube envelope in the position where the seal is made and in which:

Figure 1 represents a cross-sectional longitudinal view of a tubeenvelope, in which the lead-in wires traverse the envelope through thestembulb seal;

Fig. 2 is a top view corresponding to Fig.1; and

' Fig. 3 is a top View of an electronic tube en velope, in whicht-he-"lead-in wires are sealed through the flange of the tubularstem:

The bulb-or tube l shown in Fig. l' hasan'annular cross section 'towhichmust be sealed the flanged extremity of the exhaust tube 2, inproximity to the leading-in wires 3, embedded in a bead of glass 4 andpreviously sealed to the flange. In th manufacture of the tube l acommonrotary movement is communicated to the tube or envelope and the exhausttube 2. Then the tube is heated tangentially, at the level of its seal,by means of an extremely thin flame to a softening temperature variablefrom 700 C. to 800 C. according to the kind of glass to be shaped.

Then, by means of a graphite tool the edges of the tube are turned downon the flange. If the inward diameterv of the bulb exceeds by an in--'finitesimal amount the diameter of the stem flange, no bending isnecessary, but in every case is made, on the spot, of a certain amountof finely pulverised glass having a low melting point as shown in ionthe figure. V

Then the assembly is again rotated and heated;

so that the enamel melts and flows, thus closing the holes eventuallyexisting, and completing a' seal which ofiers a smooth surface quiteexempt of asperities.

' What I claim is:

1. The method of air-tight sealing of the finished tubular stem of aspace current tube and a bulb, the stem having the form of a flangedtube whose flange is traversed by the electrode leads and supports, thebulb being made of the same glass as the stem and having an annularcrosssection whose inside diameter is at least equal to the flangediameter, which comprises placing the stem flange in the bulb so thatthe rim of the bulb slightly overlies the, edge of the flange, heatingthe exterior face of the bulb rim to the softening temperature, bringingthis rim in close contact with the stem flange in all points of itsedge, depositing on the stem edge a layer of pulverized glass havingpractically the same dilatation coefficient as theparts to be sealed anda melting point much lower than the above-mentioned softeningtemperature and heating and melting this glass layer to form anair-tight seam between the flange and the rim of the bulb after cooling.

2. A space current tube having an air-tight glass envelope comprising, aglass stem having the form of a flanged tube, a bulb having an annularcross-section formed from the same kind of glass as the glass stem andplaced over the flanged tube so that the rim of the bulb slightlyoverlies the exterior face of the flange on the tube, and a glass seaminterposed between the, exterior face of the flange and the interioroverlying face of the glass bulb.

3. A space current tube having an air-tight glass envelope comprising aglass stem terminating in a circular flange extending in a plane normalto the axis of the stem, a glass bulb enclosing the peripheral edge ofsaid circular flange and having an inturned flattened portioncoextensive with the surface of said circular flange and encircling theexterior of said glass stem, glass beads extending transversely throughboth said flattened portion of said glass bulb and.through,,

the peripheral edge of said circular flange, leadin wires extendingthrough said glass beads and a layer of pulverized glass interposedbetween one side of said circular flange and the flattened portion ofsaid glass bulb and coextensive therewith, said pulverized glass forminga seam extending in an annular path contiguous with the flattenedportion of the glass bulb and the circular flange of said glas stem forsealing said bulb, beads and flange in an air-tight envelope.

PIERRE DUSSAUSSOY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,911,410 Xalverde May 30, 19332,188,061 Scharfnagel Jan. 23, 1940 2,248,644 Reger et al. July 8, 19412,264,183 Nash Nov. 25, 1941 2,273,437 Dunn Feb. 12, 1942 2,296,579Seelen Sept. 22, 1942 FOREIGN PATENTS Number Country Date 495,417 GreatBritain Nov. 14, 1938 OTHER REFERENCES Housekeeper-The Art of SealingBase Metals Through Glass in Journal of the American Institute ofElectrical Engineers, vol. XLII-9, 1923.

